The present invention relates to devices for delivering, dispensing, injecting, administering or infusing substances, and to methods of making and using such devices. More particularly, it relates to a device and method for detecting an occlusion in such devices, for example, in infusion pumps. Occlusions, i.e., blockages in a flow path or fluid path, must be detected as quickly as possible in portable infusion pumps to minimize the time during which, erroneously, no medicament is discharged.
The invention relates more particularly to the field of miniaturized infusion pumps which are worn by the patient permanently on his body and which ensure a (quasi)continuous delivery of medicament. A particular danger of these systems lies in possible blockages (occlusions), either of the catheter or of the infusion cannula. The resulting interruption in delivery can, if it continues, lead to a potentially life-threatening situation for the patient. If a temporary occlusion resolves itself before it is detected, the whole quantity of medicament that has been held back could be dispensed spontaneously. This overdose can likewise lead to a dangerous situation. This problem is known, for example, in the treatment of diabetes mellitus using continuous subcutaneous insulin infusion (CSII).
The detection of occlusions in portable infusion pumps takes place in the present systems by means of measuring the motor current and/or the reaction force in the gear mechanism by means of a force sensor, for example as is described in WO 0172357, U.S. Pat. No. 5,647,853 or DE 19840992. The evaluation is principally obtained by threshold comparisons for the force F exerted by the drive on the ampule stopper, or a numerical approximation of its time derivation dF/dt, for example by calculation of regression lines. These methods entail a long detection delay, because the measurements reflect an occlusion only slowly and they are dependent on a whole series of influencing variables, which can generally fluctuate within a wide range (e.g., friction of gear mechanism and ampule stopper), so that the chosen threshold values have to be high to avoid incorrect detections. With the known methods, a significant reduction in the detection delay would therefore require control of all the influencing variables in very narrow limits and would therefore be technically complex and expensive.